The most commonly used processes for imparting color to cellulosic materials are piece dyeing, continuous dyeing and yarn dyeing. In continuous dyeing, which is used primarily for fabrics that are to be a solid color, a continuous length of dry cloth is passed full-width through a trough of hot dye solution. The cloth then goes between padded rollers that squeeze in the color evenly and removes the excess liquid. In the piece dyeing method, the fabric, in a rope-like coil, is processed on a reel that passes in and out of a dye beck or vat. Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction. One of the most commonly used yarn dyeing methods is package dyeing. In this system, yarn is wound on perforated cylinders or packages and placed on vertical spindles in a round dyeing machine. In each of these referenced dyeing methods, heat, chemicals, and salts must be added to the dye bath regardless of the chemical class of the dye being used. That is, a significant amount of energy, chemicals, and salt is required in transferring dye molecules from the dye solution to the fiber as well as in swelling the fiber to render it more receptive to dyeing. Even with the best processes, only a certain percentage of the dyes are transferred to the cellulosic fabric and the excess must be washed out in subsequent steps. These processes are problematic for dye application uniformity, they use large amounts of energy and create waste water that contains residual byes, chemicals, and salts.
Since the world currently uses cotton more than any other fiber, computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy as the demand for cotton appears to be growing. However, there remains a need for efficient and robust methods of dyeing cellulosic materials.